I did find a few quotes that seem to speak to the issue of paedocommunion. I think they demonstrate that paedocommunion is a departure from the historic Reformed faith.

The first is not explicitly about paedocommunion but it does show that there was a distinction between a baptized infant and someone entitled to the full membership in the church. This is from Jonathan Edwards’The Qualifications Requisite To A Complete Standing and Full Communion: An Humble Inquiry Into The Rules Of The Word Of God Concerning The Qualifications Requisite To A Complete Standing And Full Communion In The Visible Christian Church (my emphasis):

All that acknowledge infant baptism, allow infants, who are the proper subjects of baptism, and are baptized, to be in some sort members of the Christian church. Yet none suppose them to be members in such standing as to be the proper immediate subjects of all ecclesiastical ordinances and privileges. But that some further qualifications are requisite in order to this, to be obtained, either in a course of nature, or by education, or by divine grace.

The next comes from John Calvin in his Institutes, Book 4, Chapter 16, Paragraph 30 (my emphasis):

How, pray, can we require infants to commemorate any event of which they have no understanding; how require them “to show forth the Lord’s death,” of the nature and benefit of which they have no idea? Nothing of the kind is prescribed by baptism. Wherefore, there is the greatest difference between the two signs. This also we observe in similar signs under the old dispensation. Circumcision, which, as is well known, corresponds to our baptism, was intended for infants, but the passover, for which the Supper is substituted, did not admit all kinds of guests promiscuously, but was duly eaten only by those who were of an age sufficient to ask the meaning of it (Exod. 12:26). Had these men the least particle of soundness in their brain, would they be thus blind as to a matter so very clear and obvious?